Field of the Invention
The invention relates to a method and a configuration for transmitting data over a radio interface in a radio communications system, in particular in a mobile radio system.
In radio communications systems, messages (for example voice, image information or other data) are transmitted using electromagnetic waves. The electromagnetic waves are irradiated here at carrier frequencies that lie in the frequency band provided for the respective system. In the global system for mobile communication (GSM), the carrier frequencies lie in the region of 900 MHz. For future radio communications systems, for example the universal mobile telecommunication system (UMTS) or other 3rd generation systems, frequencies in the approximately 2000 MHz frequency band are provided.
The irradiated electromagnetic waves are attenuated owing to losses resulting from reflection, refraction and irradiation due to the curvature of the earth and the like. As a result, the reception power that is available at the receiving radio station drops. The attenuation is location-dependent and also time-dependent in the case of moving radio stations.
Between a transmitting and a receiving radio station there is a radio interface over which data are transmitted using the electromagnetic waves. A subscriber separation is carried out in the GSM mobile radio system in accordance with a time division multiplex method, the so-called time division multiple access (TDMA) method which is used in combination with a frequency multiplex method, a frequency division multiple access (FDMA) method.
In the GSM mobile radio system, a TDMA frame is divided into 8 timeslots. Data relating to communications links or signaling information are transmitted as radio blocks, so-called bursts, in the timeslots, midambles with known symbols being transmitted within a radio block. The midambles can be used in the manner of training sequences for receive-end tuning of the radio station. The receiving radio station carries out an estimation of the channel pulse responses for various transmission channels by use of the midambles. Because the transmission properties of the mobile radio channel are location-dependent and frequency-dependent, the receiving radio station can carry out equalization of the received signal by use of the training sequence.
As the speed of a mobile radio station increases, the transmission properties on the radio interface also change more quickly, with the result that equalization has to be adjusted more quickly. The TDMA subscriber separation method that is used in the GSM mobile radio system is configured only for a limited speed of the mobile radio station. Above the speed limit, the transmission properties change so quickly that appropriate adjustment of the equalization is no longer possible and there is a steep increase in transmission errors. In the GSM system which operates at approximately 900 MHz this upper limit lies at approximately 250 km/h. The GSM1800 system, which is changed only in terms of its operating frequency, has at approximately 1.8 GHz, on the other hand, a speed limit which is as low as approximately 125 km/h.
For the third-generation mobile radio systems, a frequency range between approximately 2 and 2.5 GHz is provided, which would lead to a further reduction in the maximum speed using the described technology.
To permit new application areas in which mobile stations move at very high speeds, such as for example high speed trains or satellites with a low orbit, to be opened up for second-generation and third-generation mobile radio systems, more rapid adjustment of the equalization is required at the receive end of the radio stations.
Published, European Patent Application EP 0 535 403 discloses a method for receiving digital data signals which are transmitted in timeslots using the TDMA method. The digital data signals each contain a number of symbols with a training sequence of symbols. After the digital data signals are stored, channel information is respectively determined from some of the digital data signals of a first timeslot and from some of the digital data signals of a second timeslot and is subsequently combined to form an estimated channel information value. The symbols of the digital data signal of the first timeslot are subsequently equalized and demodulated with the estimated channel information value.
Published, European Patent Application EP 0 767 557 discloses a method in which at least two training sequences of receiving radio blocks of a TDMA transmission method are used by a mobile station to determine a time position of the received signal. The determined time position is subsequently used to determine the location of the mobile station. The mobile station uses training sequences in radio blocks of its own communications link here or its own communications link and additionally one or more training sequences of further communications links which are known in the mobile station.
International Patent Disclosure WO 96/11533 discloses a method for signal detection in a TDMA system. In this method, multipath channel estimations for a first signal and at least of one further interference signal are determined using received training sequences. The first signal is subsequently detected using both the channel estimation of the first signal and the channel estimation of the further signal.
U.S. Pat. No. 5,185,764 discloses a receiver for receiving distorted data signals which vary over time. The receiver has, inter alia, a channel estimator that generates a channel information signal by use of a training signal that is transmitted together with the data signals, and by use of a representation of the training signal which is stored in the receiver.